Biological contactors that float in wastewater lagoons and enclose and aerate media supporting growth of aerobic bacteria
Floating biological contactors such as shown in U.S. Pat. Nos. 5,228,998 and 6,022,476 are valuable in promoting growth of aerobic bacteria to consume organic solids in wastewater lagoons. Such contactors float in a lagoon where they confine a volume of bacteria supporting media in a submerged container. They also establish liquid flow and aeration to encourage aerobic bacteria growth on a large surface area of the submerged media.
Although previously known biological contactors have succeeded to some extent, they have consumed considerable energy and have required expensive maintenance so that their cost effectiveness has left room for improvement. This invention brings a needed improvement to floating biological contactors making them more efficient in sustaining growth of a large bacterial colony and less expensive to operate and maintain.
The inventive improvement to a floating biological contactor involves a better fluid flow system. First, the bottom of a submerged container confining aerobic bacteria growth media is provided with openings small enough to prevent the media from falling downward into the lagoon and large enough to allow liquid from the lagoon to flow upward through the openings and upward through the submerged media confined within the container above the openings. Walls of the container above the bottom also have openings allowing upflowing liquid to flow out through the walls and back into the lagoon. This allows a gentle flow of liquid that is preferably motivated by air bubbles rising from air diffusers arranged under the media in the region of the container bottom. Air bubbles rising from the diffusers draw or entrain liquid from below the container so that liquid moves upward through the container bottom to establish a gentle rising flow that circulates lagoon liquid through the media. The rising bubbles also provide the air necessary to help the aerobic bacteria grow and thrive on the extensive surface area of the confined media.
The bottom openings in the submerged media container also allow downward settlement of solid particles dropping downward from the media. Such solid particles can fall through the bottom openings and settle to the bottom of the lagoon.
Preferably, coarse bubble dispensers are also arranged under the media near the bottom of the container to drive coarse air bubbles up through the media during a cleaning cycle. The coarse air bubbles rise with sufficient force to agitate the media and knock loose solid particles that settle from the media and pass downward through the bottom openings of the container.
A compressor and an air delivery system preferably supplies the air necessary for both the fine bubble diffusers and the coarse bubble dispensers. Since more compressor capacity is necessary for coarse bubble agitation, a preferred compressor has more capacity than necessary for supplying only the fine bubble diffusers. This excess capacity is preferably used to deliver air to additional diffusers arranged outboard of the media chamber for aerating lagoon water in the vicinity of the float. A valving system switches the air flow between coarse bubble dispensers and fine bubble diffusers so that coarse bubbles are formed only during cleaning cycles.